Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/templates/partials/message_attachment.css

@@ -0,0 +1,146 @@
+.messageAttachments * {
+    font-family: Open Sans, sans-serif !important;
+}
+
+.messageAttachmentContent {
+    padding: 0px;
+    border: 1px solid rgba(63, 67, 80, 0.16);
+    margin-bottom: 20px;
+    border-radius: 0 4px 4px 0;
+}
+
+.messageAttachmentContent > table, .attachment__body {
+    font-family: Open Sans, sans-serif;
+    text-align: left;
+    font-size: 14px;
+    line-height: 20px;
+    color: #3F4350;
+}
+
+.messageAttachmentContent .attachment__author-icon {
+    width: 14px;
+    height: 14px;
+    margin-right: 5px;
+    border-radius: 50px;
+    vertical-align: middle;
+}
+
+.attachment__author-name {
+    opacity: 0.6;
+}
+
+.messageAttachmentContent p {
+    margin: 0;
+}
+
+.attachment__title {
+    padding: 0;
+    margin: 5px 0;
+    font-size: 14px;
+    font-weight: 600;
+    line-height: 18px;
+}
+
+.attachment__image {
+    max-height: 300px;
+    border: 1px solid transparent;
+    margin-bottom: 1em;
+}
+
+
+.attachment__thumb-image {
+    max-width: 100%;
+    max-height: 75px;
+}
+
+.attachment__thumb-container {
+    max-width: 80px;
+    width: max-content;
+}
+
+.attachment__wrapper {
+    width: 100%;
+    display: flex;
+    flex-direction: row;
+    gap: 12px;
+}
+
+.attachment__body {
+    flex: 1;
+}
+
+.messageAttachmentContent > table.attachment__footer-container {
+    color: #a3a3a3;
+    font-size: 12px;
+}
+
+.attachment__footer-icon {
+    width: 16px;
+    height: 16px;
+}
+
+.attachment__footer-container {
+    color: #a3a3a3;
+    font-size: 12px;
+}
+
+.messageAttachment_title {
+    padding-top: 1em;
+    font-weight: 600;
+    margin-bottom: 4px;
+}
+
+.pretext h1 {
+    font-size: 28px;
+    line-height: 32px;
+}
+
+.pretext h2 {
+    font-size: 25px;
+    line-height: 30px;
+}
+
+.pretext h3 {
+    font-size: 22px;
+    line-height: 25px;
+}
+
+.pretext h4 {
+    font-size: 19px;
+    line-height: 24px;
+}
+
+.pretext h5 {
+    font-size: 15px;
+    line-height: 20px;
+}
+
+.pretext h6 {
+    font-size: 1em;
+    line-height: 1.4em;
+}
+
+.pretext > * {
+    margin-bottom: 16px;
+}
+
+.messageAttachments {
+    margin-top: 22px;
+}
+
+.messageAttachments h1, h2, h3, h4, h5, h6 {
+    font-weight: 500;
+}
+
+code {
+    padding: 2px 4px;
+    font-size: 90%;
+    background-color: rgba(63, 67, 80, 0.1);
+    border-radius: 4px;
+}
+
+.messageAttachments a {
+    background-color: unset !important;
+    border: none !important;
+    padding: unset !important;
+}